1. Field of the Invention:
The present invention relates to a circuit arrangement for a digital telephone station in digital telephone systems, particularly private branch exchanges (PBX's), whereby the telephone station is controlled by a microprocessor and whereby inquiry and control signals are constantly exchanged via the leads of the subscriber line, whereby, furthermore, the feed voltage supply of the telephone station in the quiescent condition and in the voice condition occurs via the subscriber line or via a local voltage source, and whereby the cradle switch contact, in its actuated condition, connects a first control input of the microprocessor to ground via a first ohmic resistor.
2. Description of the Prior Art
Prior known telephone stations are fundamentally controlled by one or more microprocessors. Inquiry and control events, via the subscriber line, are thereby also sequenced during the quiescent condition of the telephone station when, for example, the handset is picked up at such a telephone station and the cradle switch contact is actuated as a result thereof, the microprocessor recognizes this event via a control input during a routine interrogation and interprets the same.
Given disturbing influences, however, such microprocessors tend to block, so that an interrogation no longer occurs and, therefore, a connection cannot be produced after the handset is lifted. It is necessary to reset the microprocessor to an initial position via its reset input, or in some other form, and to allow the microprocessor to restart. This was heretofore carried out in that, for example, a resetting was effected on the basis of a brief disconnection of the local feed or of the remote feed.